An ammeter of resistance \( 5\,\Omega \) reads up to 1 A. The value of the shunt required to increase its range to 5 A will be
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 1.25\,\Omega \)
A shunt is a small resistance connected in parallel with the ammeter. It carries the extra current, so that the ammeter still carries only \( 1\,\mathrm{A} \) when the total current is \( 5\,\mathrm{A} \). The two are in parallel, so they have the same potential difference.
\( I_g = 1\,\mathrm{A} \)
\( G = 5\,\Omega \)
\( I = 5\,\mathrm{A} \)
\( \displaystyle I_g\,G = (I - I_g)\,S \)
\( \displaystyle S = \frac{I_g\,G}{I - I_g} = \frac{1 \times 5}{5 - 1} = 1.25\,\Omega \)